OpenGL ES3.0 EGL创建表面和渲染上下文流程

1. eglGetError是全程调用API时，若调用失败，用来获取失败原因的，所以单独列出。
2. eglChooseConfig是让EGL自动帮你选择合适的配置，结果往往跟手动调用eglGetConfigs和eglGetConfigAttrib得到的结果相同，下面的代码就是使用eglChooseConfig。

例程：

//  esCreateWindow()
//
//      title - name for title bar of window
//      width - width of window to create
//      height - height of window to create
//      flags  - bitwise or of window creation flags
//          ES_WINDOW_ALPHA       - specifies that the framebuffer should have alpha
//          ES_WINDOW_DEPTH       - specifies that a depth buffer should be created
//          ES_WINDOW_STENCIL     - specifies that a stencil buffer should be created
//          ES_WINDOW_MULTISAMPLE - specifies that a multi-sample buffer should be created
//
GLboolean ESUTIL_API esCreateWindow ( ESContext *esContext, const char *title, GLint width, GLint height, GLuint flags )
{
#ifndef __APPLE__
   EGLConfig config;
   EGLint majorVersion;
   EGLint minorVersion;
   EGLint contextAttribs[] = { EGL_CONTEXT_CLIENT_VERSION, 3, EGL_NONE };

   if ( esContext == NULL )
   {
      return GL_FALSE;
   }

#ifdef ANDROID
   // For Android, get the width/height from the window rather than what the
   // application requested.
   esContext->width = ANativeWindow_getWidth ( esContext->eglNativeWindow );
   esContext->height = ANativeWindow_getHeight ( esContext->eglNativeWindow );
#else
   esContext->width = width;
   esContext->height = height;
#endif

   if ( !WinCreate ( esContext, title ) )
   {
      return GL_FALSE;
   }

   esContext->eglDisplay = eglGetDisplay( esContext->eglNativeDisplay );
   if ( esContext->eglDisplay == EGL_NO_DISPLAY )
   {
      return GL_FALSE;
   }

   // Initialize EGL
   if ( !eglInitialize ( esContext->eglDisplay, &majorVersion, &minorVersion ) )
   {
      return GL_FALSE;
   }

   {
      EGLint numConfigs = 0;
      EGLint attribList[] =
      {
         EGL_RED_SIZE,       5,
         EGL_GREEN_SIZE,     6,
         EGL_BLUE_SIZE,      5,
         EGL_ALPHA_SIZE,     ( flags & ES_WINDOW_ALPHA ) ? 8 : EGL_DONT_CARE,
         EGL_DEPTH_SIZE,     ( flags & ES_WINDOW_DEPTH ) ? 8 : EGL_DONT_CARE,
         EGL_STENCIL_SIZE,   ( flags & ES_WINDOW_STENCIL ) ? 8 : EGL_DONT_CARE,
         EGL_SAMPLE_BUFFERS, ( flags & ES_WINDOW_MULTISAMPLE ) ? 1 : 0,
         // if EGL_KHR_create_context extension is supported, then we will use
         // EGL_OPENGL_ES3_BIT_KHR instead of EGL_OPENGL_ES2_BIT in the attribute list
         EGL_RENDERABLE_TYPE, GetContextRenderableType ( esContext->eglDisplay ),
         EGL_NONE
      };

      // Choose config
      if ( !eglChooseConfig ( esContext->eglDisplay, attribList, &config, 1, &numConfigs ) )
      {
         return GL_FALSE;
      }

      if ( numConfigs < 1 )
      {
         return GL_FALSE;
      }
   }


#ifdef ANDROID
   // For Android, need to get the EGL_NATIVE_VISUAL_ID and set it using ANativeWindow_setBuffersGeometry
   {
      EGLint format = 0;
      eglGetConfigAttrib ( esContext->eglDisplay, config, EGL_NATIVE_VISUAL_ID, &format );
      ANativeWindow_setBuffersGeometry ( esContext->eglNativeWindow, 0, 0, format );
   }
#endif // ANDROID

   // Create a surface
   esContext->eglSurface = eglCreateWindowSurface ( esContext->eglDisplay, config, 
                                                    esContext->eglNativeWindow, NULL );

   if ( esContext->eglSurface == EGL_NO_SURFACE )
   {
      return GL_FALSE;
   }

   // Create a GL context
   esContext->eglContext = eglCreateContext ( esContext->eglDisplay, config, 
                                              EGL_NO_CONTEXT, contextAttribs );

   if ( esContext->eglContext == EGL_NO_CONTEXT )
   {
      return GL_FALSE;
   }

   // Make the context current
   if ( !eglMakeCurrent ( esContext->eglDisplay, esContext->eglSurface, 
                          esContext->eglSurface, esContext->eglContext ) )
   {
      return GL_FALSE;
   }

#endif // #ifndef __APPLE__

   return GL_TRUE;
}